Fig. 879. The external and internal mutilated cog-wheels work alternately into the pinion, and give slow forward and quick reverse motion.

Figs. 880, 881. These are parts of the same movement, which has been used for giving the roller motion in wool-combing machines. The roller to winch the wheel F, Fig. 8S1, is secured, is required to make 1/3 revolution backward, then 2/3 revolution forward, when it must stop until another length of combed fibre is ready for delivery. This is accomplished by the grooved heart-cam C, D, B, e, Fig. 880, the stud A working in the said groove; from C to D it moves the roller backward, and from D to e it moves it forward, the motion being transmitted through the catch G, to the notch-wheel F, on the roller-shaft H. When the stud A arrives at the point e in the cam, a projection at the back of the wheel which carries the cam strikes the projecting piece on the catch G, and raises it out of the notch in the wheel F, so that while the stud is travelling in the cam from e to C, the catch is passing over the plain surface between the two notches in the wheel F, without imparting any motion; but when stud A arrives at the part C, the catch has dropped in another notch and is again ready to move wheel F and roller as required.

Fig. 882. An arrangement for obtaining variable circular motion. The sectors are arranged on different planes, and the relative velocity changes according to the respective diameters of the sectors.

Fig. 883. Intermittent circular motion of the ratchet-wheel from vibratory motion of the arm carrying a pawl.

Fig. 884. Drag-link motion. Circular motion is transmitted from one crank to the other.

Fig. 885. This represents an expanding pulley. On turning pinion d to the right or left, a similar motion is imparted to wheel c, which, by means of curved slots cut therein, thrust the studs fastened to arms of pulley outward or inward, thus augmenting or diminishing the size of the pulley.

Fig. 886 represents a chain and chain pulley. The links being in different planes, spaces are left between them for the teeth of the pulley to enter.

Fig. 887. Another kind of chain and pulley.

Fig. 888. Another variety.

Fig. 889 shows two different kinds of stops for a lantern-wheel.

Fig. 890. Transmitted circular motion. The connecting rods are so arranged that when one pair of connected links is over the dead-point, or at the extremity of its stroke, the other is at right angles; continuous motion is thus ensured without a fly-wheel.

Mechanical Movements Part 9 888Mechanical Movements Part 9 889Mechanical Movements Part 9 890Mechanical Movements Part 9 891Mechanical Movements Part 9 892Mechanical Movements Part 9 893Mechanical Movements Part 9 894Mechanical Movements Part 9 895Mechanical Movements Part 9 896Mechanical Movements Part 9 897

Fig. 891. Intermittent circular motion is imparted to the toothed wheel by vibrating the arm B. When the arm B is lifted, the pawl C is raised from between the teeth of the wheel, and travelling backward over the circumference again drops between two teeth on lowering the arm, and draws with it the wheel.

Fig. 892. The oscillating of the tappet-arm produces an intermittent rotary motion of the ratchet-wheel. The small spring at the bottom of the tappet-arm keeps the tappet in the position shown in the drawing, as the arm rises, yet allows it to pass the teeth on the return motion.

Fig. 893. A nearly continuous circular motion is imparted to the ratchet-wheel on vibrating the lever a, to which the 2 pawls b and c are attached.

Fig. 894. An arrangement of stops for a spur-gear.

Fig. 895. A reciprocating circular motion of the top arm makes its attached pawl produce an intermittent circular motion of the crown-ratchet, or rag-wheel.

Fig. 896 represents varieties of stops for a ratchet-wheel.

Fig. 897. Intermittent circular motion is imparted to the wheel A by the continuous circular motion of the smaller wheel with one tooth.

Fig. 898. A brake used in cranes and hoisting machines. By pulling down the end of the lever, the ends of the brake-strap are drawn towards each other, and the strap tightened on the brake-wheel.

Fig. 899. A dynamometer, or instrument used for ascertaining the amount of useful effect given out by any motive power. It is used as follows; - A is a smoothly-turned pulley, secured on a shaft as near as possible to the motive power. Two blocks of wood are fitted to this pulley, or one block of wood and a series of straps fastened to a band or chain, as in the drawing, instead of a common block. The blocks, or block and straps, are so arranged that they may be made to bite or press upon the pulley by means of the screws and nuts on the top of the lever D. To estimate the amount of power transmitted through the shaft, it is only necessary to ascertain the amount of friction of the drum A when it is in motion, and the number of revolutions made. At the end of the lever D is hung a scale B, in which weights are placed. The two stops C, C, are to maintain the lever as nearly as possible in a horizontal position. Now, suppose the shaft to be in motion, the screws are to be tightened and weights added in B, until the lever takes the position shown in the drawing, at the required number of revolutions.

Therefore, the useful effect would be equal to the product of the weights, multiplied by the velocity at which the point of suspension of the weights would revolve if the lever were attached to the shaft.